Earlier McGregor, 32, said on Twitter he was "boxing Manny Pacquiao next in the Middle East."
"It will be a true honour to have faced two of the greatest boxers of the modern era," McGregor added, referencing his famous 2017 clash against the undefeated Floyd Mayweather.
Pacquiao, 41, has not fought since claiming the WBA welterweight crown with a stunning victory over Keith Thurman in Las Vegas in July last year.
A bout against McGregor, who faced welterweight king Mayweather in a money-spinning fight three years ago, would guarantee Pacquiao another lucrative payday as he nears the end of an illustrious boxing career.
Despite his technical knockout loss to Mayweather in his boxing debut, McGregor had shown that he was capable of challenging "the best boxers in the world", Gibbons said.
"Our lawyers are finalising all the confidential details, but both fighters are getting ready for this one epic last boxing fight," Joson said.
McGregor has not fought since beating Donald Cerrone at UFC 246 in January, and has previously expressed his sadness at being kept out of the Octagon because of Covid-19.
The UFC's biggest cash cow would essentially be wasted at an event without crowds, so the promotion's president Dana White is keeping McGregor on ice for now.
The Irishman uploaded footage of himself shadow boxing in a ring yesterday, and also posted a picture to his Instagram story of a promotional poster featuring him alongside Pacquiao, spruiking a Middle East bout in the winter of 2020.
White recently said he and McGregor were working on "some fun stuff" for the future.
Pacquiao has successfully combined a political career in the Philippines, where he is an elected senator, while continuing to box at the highest level.
He had turned pro in his teens 25 years ago and owns a 62-7-2 win-loss-draw record with 39 knockouts.
"His main focus right now is to help here and there, providing relief, shelter, money and food, among other necessities," Joson said.
The virus has infected 301,000 people in the Philippines and killed more than 5000.